svn commit: r278154 - head/lib/msun/src

[Steve Kargl]

On Wed, Feb 04, 2015 at 02:38:40AM +1100, Bruce Evans wrote:
> On Tue, 3 Feb 2015, Pedro F. Giffuni wrote:
> 
> > Log:
> >  Reduce confusion in scalbnl() family of functions.
> >
> >  The changes unrelated to the bug in r277948 made
> >  the code very difficult to understand to both
> >  coverity and regular humans so take a step back
> >  to something that is much easier to understand
> >  for both and follows better the original code.
> > 
> >  CID:	1267992, 1267993, 1267994
> >  Discussed with:	kargl
> 
> You mean, take a step backwards to something that is harder to understand.
> 

Well, the correct fix should have been to ONLY fix the typo,
and leave the code rewrite for a second commit.

Index: s_scalbln.c
===================================================================
--- s_scalbln.c (revision 276768)
+++ s_scalbln.c (working copy)
@@ -72,5 +72,5 @@
                else
                        in = INT_MIN;
        }
-       return (scalbnl(x, (int)n));
+       return (scalbnl(x, in));
 }

But, that's water under the bridge.

You forgot to include a diff.  Here's one untested attempt at 
addressing your concerns.  

-- 
Steve

Index: s_scalbln.c
===================================================================
--- s_scalbln.c	(revision 276768)
+++ s_scalbln.c	(working copy)
@@ -27,21 +27,23 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
-#include <limits.h>
+#include <float.h>
 #include <math.h>
 
+#define	FLT_LARGE	FLT_MAX_EXP - FLT_MIN_EXP + FLT_MANT_DIG
+#define	FLT_SMALL	FLT_MIN_EXP - FLT_MAX_EXP
+#define	DBL_LARGE	DBL_MAX_EXP - DBL_MIN_EXP + DBL_MANT_DIG
+#define	DBL_SMALL	DBL_MIN_EXP - DBL_MAX_EXP
+#define	LDBL_LARGE	LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG
+#define	LDBL_SMALL	LDBL_MIN_EXP - LDBL_MAX_EXP
+
 double
 scalbln (double x, long n)
 {
 	int in;
 
-	in = (int)n;
-	if (in != n) {
-		if (n > 0)
-			in = INT_MAX;
-		else
-			in = INT_MIN;
-	}
+	in = n > DBL_LARGE ? DBL_LARGE : n < DBL_SMALL ? DBL_SMALL : n;
+
 	return (scalbn(x, in));
 }
 
@@ -50,27 +52,16 @@
 {
 	int in;
 
-	in = (int)n;
-	if (in != n) {
-		if (n > 0)
-			in = INT_MAX;
-		else
-			in = INT_MIN;
-	}
+	in = n > FLT_LARGE ? FLT_LARGE : n < FLT_SMALL ? FLT_SMALL : n;
+
 	return (scalbnf(x, in));
 }
-
 long double
 scalblnl (long double x, long n)
 {
 	int in;
 
-	in = (int)n;
-	if (in != n) {
-		if (n > 0)
-			in = INT_MAX;
-		else
-			in = INT_MIN;
-	}
-	return (scalbnl(x, (int)n));
+	in = n > LDBL_LARGE ? LDBL_LARGE : n < LDBL_SMALL ? LDBL_SMALL : n;
+        
+	return (scalbnl(x, in));
 }